U.S. patent number 6,564,653 [Application Number 09/966,196] was granted by the patent office on 2003-05-20 for device for measuring torque applied to a turning shaft.
This patent grant is currently assigned to The Torrington Company. Invention is credited to Pascal Desbiolles.
United States Patent |
6,564,653 |
Desbiolles |
May 20, 2003 |
Device for measuring torque applied to a turning shaft
Abstract
A test body deformable upon application of torque to a turning
shaft. First and second bearings with the turning collar of the
first bearing being connected near a first end of the test body and
the turning collar of the second bearing being connected near a
second end of the test body. Each bearing is equipped with a
digital device for determining the angular position of the turning
collar relative to the fixed collar. Each digital device includes
an annular device for generating magnetic pulses, mounted for
turning jointly with the turning collar, and a fixed magnetic
sensor for detecting the magnetic pulses and for delivering digital
signals. An electronic device processes digital signals from the
magnetic sensors to determine the angular position of the annular
devices, and a comparison device compares the digital signals to
ascertain the torque applied to the turning shaft.
Inventors: |
Desbiolles; Pascal (Glieres,
FR) |
Assignee: |
The Torrington Company
(Torrington, CT)
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Family
ID: |
8855967 |
Appl.
No.: |
09/966,196 |
Filed: |
September 28, 2001 |
Foreign Application Priority Data
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Oct 31, 2000 [FR] |
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00 14014 |
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Current U.S.
Class: |
73/862.335 |
Current CPC
Class: |
G01L
3/104 (20130101); G01L 3/109 (20130101) |
Current International
Class: |
G01L
3/10 (20060101); G01L 003/02 () |
Field of
Search: |
;73/862.328,862.331,862.332,862.333,862.334,862.335,862.336 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2769087 |
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Sep 1997 |
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FR |
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2769088 |
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Sep 1997 |
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FR |
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Primary Examiner: Noori; Max
Attorney, Agent or Firm: Michael Best & Friedrich
LLP
Claims
Having described the invention, what is claimed is:
1. A device for measuring torque applied to a turning shaft, the
device comprising: a test body that is deformable with torsion upon
application of torque to the shaft; first and second bearings, each
bearing having a fixed collar, a turning collar, and rolling bodies
arranged between them, the turning collar of the first bearing
being connected with the test body near a first end of the test
body, the turning collar of the second bearing being connected with
the test body near a second end of the test body; the first and
second bearings each being equipped with a digital device for
determining angular position of the turning collar in relation to
the fixed collar, with the digital devices including an annular
means for generating magnetic pulses, mounted for turning jointly
with the turning collar, and a fixed magnetic sensor for detecting
the magnetic pulses and for delivering digital signals; electronic
means for processing digital signals from the magnetic sensors,
capable of determining the angular position of the annular means;
and a comparison device for comparing digital signals derived,
respectively, from each of the electronic means for ascertaining
the value of the torque applied to the turning shaft.
2. The device according to claim 1, wherein the sensors comprise at
least two sensing elements chosen from the group of Hall-effect
probes, magnetoresistance elements, and giant magnetoresistances
elements.
3. A device according to claim 1, wherein the annular means that
generates pulses is a multipole ring of synthetic material loaded
with particles of ferrite formed with several contiguous magnetic
fields with inverted direction of magnetization of a given magnetic
field in relation to two contiguous magnetic fields.
4. A device according to claim 1, wherein the comparison device
compares two relative angles.
5. A device according to claim 1, wherein the comparison device
compares two absolute angles.
6. A device according to claim 1, wherein at least one of the
determination devices is also used for determining angular position
of the turning shaft.
7. A device according to claim 6, wherein at least one of the
determination devices ascertains absolute position of the turning
collar in relation to the fixed collar.
8. A device according to claim 1, wherein the determination devices
each comprise an interpolator that increases resolution of
respective output signals.
9. A device according to claim 1, wherein the determination devices
each comprise a register that is initialized at zero under zero
torque.
10. A device according to claim 9, wherein the comparison device
comprises a subtracter for subtracting a value of the registers to
ascertain the torque applied to the turning shaft.
11. A device according to claim 1, wherein the electronic means and
the comparison device are integrated in a control computer.
12. A device according to claim 1, wherein the test body is
integrated with the turning shaft, the test body being in the form
of a zone of reduced diameter originating from material of the
turning shaft.
13. A device according to claim 1, wherein the fixed magnetic
sensor is integrated with the first and second bearings.
14. A module for measuring torque applied to a turning shaft, the
module comprising: a test body that is deformable with torsion upon
application of torque to the shaft; first and second bearings, each
bearing having a fixed collar, a turning collar, and rolling bodies
arranged between them, the turning collar of the first bearing
being connected with the test body near a first end of the test
body, the turning collar of the second bearing being connected with
the test body near a second end of the test body; the first and
second bearings each being equipped with a digital device for
determining angular position of the turning collar in relation to
the fixed collar, with the digital devices including an annular
means for generating magnetic pulses, mounted for turning jointly
with the turning collar, and a fixed magnetic sensor for detecting
the magnetic pulses and for delivering digital signals; electronic
means for processing digital signals from the magnetic sensors,
capable of determining the angular position of the annular means; a
comparison device for comparing digital signals derived,
respectively, from each of the electronic means for ascertaining
the value of the torque applied to the turning shaft; and means of
connection with, respectively, two parts of the turning shaft, with
the turning shaft lacking the test body.
15. A module for measuring torque applied to a turning shaft, the
module comprising: a test body that is deformable with torsion upon
application of torque to the shaft; first and second bearings, each
bearing having a fixed collar, a turning collar, and rolling bodies
arranged between them, the turning collar of the first bearing
being connected with the test body near a first end of the test
body, the turning collar of the second bearing being connected with
the test body near a second end of the test body; the first and
second bearings each being equipped with a digital device for
determining angular position of the turning collar in relation to
the fixed collar, with the digital devices including an annular
means for generating magnetic pulses, mounted for turning jointly
with the turning collar, and a fixed magnetic sensor for detecting
the magnetic pulses and for delivering digital signals; electronic
means for processing digital signals from the magnetic sensors,
capable of determining the angular position of the annular means; a
comparison device for comparing digital signals derived,
respectively, from each of the electronic means for ascertaining
the value of the torque applied to the turning shaft; and means of
connection with one end of the turning shaft and with a component
applying the torque, with the turning shaft lacking the test
body.
16. A measuring module according to claim 14, wherein the magnetic
sensors are separate from the first and second bearings.
17. A measuring module according to claim 15, wherein the magnetic
sensors are separate from the first and second bearings.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to devices for measuring torque
applied to a turning shaft and, more particularly, to devices for
measuring torque applied to a steering column of a vehicle through
a steering wheel.
Conventionally, a steering column is designed as a tubular element,
fixed to the body of a vehicle under the instrument panel, that
guides and supports a transmission shaft connected to the steering
wheel. The steering wheel is then a manual control component,
connected to the steered wheels and used by the driver for steering
the vehicle.
The invention also concerns decoupled steering columns. In contrast
to conventional steering columns, decoupled steering columns are
not connected with a steering box transforming the circular
movement of the steering wheel into angular displacement of the
drop arm, that causes steering of the wheels. Quite the reverse,
with decoupled steering there is no direct mechanical connection
between the steering wheel and the wheels resting on the ground,
whether the vehicle is real or belongs to a simulation system. This
simulation can have the goal of games, in connection with training
in automobile driving schools or even in connection with an
interactive driving simulation for the needs of automobile
manufacturers.
In such simulators, the interpretation of force at the steering
wheel as a result of a mechanism generating a resisting torque on
the steering wheel according to the type of vehicle to be
simulated, which may or may not be equipped with power-assisted
steering, must take into account the conditions to be recreated.
The measurement of the torque applied to the steering wheel is
consequently essential for ensuring good simulation in real
time.
The measurement of the torque on the shaft of the steering wheel is
also very important in power steering or power-assisted steering.
In fact, the triggering of the assistance particularly depends on
the torque applied to the steering wheel by the driver. The device
for measuring the torque used in power steering produces a signal
indicative of steering torque exerted by the driver on the steering
wheel, and therefore on the transmission shaft of the steering
column of the vehicle. This signal is conventionally addressed at a
steering assistance computer that triggers the assistance by
controlling, for example, an electric motor, in the case of
electric power steering.
Measuring devices of the torque applied to the turning shaft are
already known, and consist of a torsion bar in which an output
signal is the analog type that is proportional to the magnetic
field. For example, the detection of the angular displacement of
two magnetic field generators in relation to detecting devices
makes it possible to deliver an analog signal proportional to the
torque applied. This type of analog magnetic technology has a
number of drawbacks, in particular regarding the control of the air
gap and the temperature balance of the magnetic field.
Within the scope of torque measuring devices of the prior art, the
control of the air gap and drifts in temperature complicate the
assembly because of the number of mechanical parts to be assembled
and the precise placement of the magnetic transitions in relation
to the detecting devices, which requires a phase for calibrating
and regulating during assembly of the device. Furthermore, torque
measuring devices of the prior art do not integrate bearings
necessary for rotation of the turning shaft, which make the shaft
and torque measuring device more complex to assemble.
The foregoing illustrates limitations known to exist in present
devices and methods. Thus, it is apparent that it would be
advantageous to provide an alternative directed to overcoming one
of more of the limitations set forth above. Accordingly, a suitable
alternative is provided including features more fully disclosed
hereinafter.
SUMMARY OF THE INVENTION
In one aspect of the invention, this is accomplished by providing a
device for measuring torque applied to a turning shaft, the device
comprising a test body that is deformable with torsion upon
application of torque to the shaft and first and second bearings.
Each bearing has a fixed collar, a turning collar, and rolling
bodies arranged between them, the turning collar of the first
bearing being connected with the test body near a first end of the
test body, the turning collar of the second bearing being connected
with the test body near a second end of the test body. The first
and second bearings each are equipped with a digital device for
determining angular position of the turning collar in relation to
the fixed collar, with the digital devices including an annular
means for generating magnetic pulses, mounted for turning jointly
with the turning collar, and a fixed magnetic sensor for detecting
the magnetic pulses and for delivering digital signals. An
electronic means for processing digital signals from the magnetic
sensors to determine the angular position of the annular means. A
comparison device compares digital signals derived, respectively,
from each of the electronic means to ascertain the torque applied
to the turning shaft.
According to a second aspect of the invention, this is accomplished
by providing a module for measuring torque applied to a turning
shaft, with the module consisting of a device such as that
described above and a means of connecting the module with,
respectively, two parts of the turning shaft, with the turning
shaft lacking a test body.
According to a third aspect of the invention, this is accomplished
by providing a module for measuring torque applied to a turning
shaft, with the module comprising a device such as that described
above and a means of connecting the module with, respectively, one
end of the turning shaft and the component applying the torque,
with the turning shaft lacking a test body.
The foregoing and other aspects will become apparent from the
following detailed description of the invention when considered in
conjunction with the accompanying
BRIEF DESCRIPTION OF THE DRAWING FIGURES
FIG. 1 is a functional diagram of a measuring device of the torque
applied to a turning shaft showing the two multipole rings
connected respectively with a turning collar of a bearing; the two
fixed magnetic sensors each deliver two signals that are treated
respectively by an electronic means so as to determine the angular
position of each of the two multipole rings, with the comparison
device delivering the value of the torque applied to the turning
shaft;
FIG. 2 is a partial view in longitudinal section of a steering
column integrating a device for measuring torque applied to the
steering column; and
FIG. 3 is a perspective view, partially exploded and partially torn
away, of a module for measuring torque applied to a turning
shaft.
DETAILED DESCRIPTION
FIGS. 1 through 3 represent a measuring device of torque applied to
a turning shaft 1 of the type consisting of a test body 2 that is
deformable with torsion under the action of the torque applied to
shaft 1. In a specific example (see FIG. 2), the turning shaft 1 is
a steering column of a vehicle on which steering torque is exerted
by the driver with the aid of the steering wheel.
To determine this steering torque, it is known that a test body 2
may be provided that is capable of transmitting applied torque by
being elastically deformed under the action of the torque. The
measurement of the torque exerted can then be processed,
particularly in the form of an electric signal, with a steering
assistance computer that triggers the assistance, for example,
through an electric motor in the case of electric power
steering.
The test body 2 is typically presented in the form of a torsion bar
with reduced diameter in relation to that of the shaft 1 because,
with isotropic linear elasticity, the torque exerted in pure
torsion on a complete cylindrical bar with a circular cross section
varies for a given material, according to the fourth power of the
diameter of the bar with a fixed torsion angle. Consequently, the
fact of forming a zone with a reduced cross section, under the
effect of the torque applied, makes it possible to concentrate and
amplify the deformations in torsion on said zone so as to form from
it a preferred zone for the value of the torque.
In the embodiment methods represented in the figures, the torsion
bar 2, arranged coaxially with the shaft 1, is cylindrical in cross
section. However, to facilitate particular applications, the
arrangement of the torsion bar 2 and/or the geometry of the cross
section can be provided differently. The test body 2 presents a
first 3 and a second 4 end that, under the effect of the torque
applied to the shaft 1, are displaced by rotating jointly with the
shaft 1, but with an angular displacement of one compared with the
other.
It is desired to measure this angular displacement in order to
calculate the torque applied to the shaft 1 by electronic means,
taking into account the nature of the test body. For this purpose,
a first 5 and second 6 bearing are provided, respectively, near the
first 3 and the second 4 ends of the test body 2 and opposite each
other. These bearings 5, 6 are those usually used to enable
rotation of a turning shaft 1; namely, they are of the type
consisting of a fixed exterior collar 7, a turning interior collar
8, and rolling bodies 9 arranged between them.
According to the invention, the bearings 5, 6 are each equipped
with a device 10 that determines the angular position of the
turning collar 8 in relation to the fixed collar 7. In the
embodiments represented in FIGS. 2 and 3, the bearings 5, 6 are
identical and are arranged opposite each other; however, different
bearings 5, 6 can be supplied, provided that they are constructed
to enable the measurement of the angular position of the turning
collar 8, and therefore that of the end 3, 4 of the test body 2
with which it is connected.
In relation to FIG. 1, digital determination devices 10 are
described, each consisting of an annular means 11 generating
magnetic pulses combined with the turning collar 8 to turn jointly
with it; a magnetic sensor 12 fixed in relation to the turning
shaft 1, and which is constructed to detect said magnetic pulses
and to deliver digital signals S1, S2; and electronic means 13
capable of determining the angular position of the annular means 11
from the digital signals derived from said magnetic sensor 12. Such
devices 10 are, for example, described in documents FR-A-2,769,087
and FR-A-2,769,088 from the applicant, and, accordingly,
descriptions will not be repeated here.
Sensors 12 consist of, for example, at least two sensing elements
or a block of sensing elements chosen from the group consisting of
Hall-effect probes, magnetoresistances elements and, giant
magnetoresistances elements, with sensing elements being placed
opposite the air gap of the annular means 11 generating magnetic
pulses. In a specific example, the means 11 for generating pulses
is formed from a multipole ring of synthetic material loaded with
particles of ferrite formed with several contiguous fields 14 with
inverted direction of magnetization of a given field by comparison
with the two fields that are contiguous with it.
According to this embodiment, the sensors 12 produce at least two
electric signals that are sinusoidal in form, of the same
amplitude, centered on the same average value, and in quadrature
with each other. Furthermore, they have a period equal to one
rotating turn of the ring, or 2.pi. mechanics. From these signals,
and as described respectively in the documents FR-A-2,769,087 and
FR-A-2,769,088, it is possible to obtain digital signals S1 and S2
that make it possible, through electronic means 13, to determine
the relative or absolute position of the ring 11, and therefore the
connected turning collar 8, in relation to the fixed collar 7.
Relative angular position of a turning component is understood to
be the angle separating the position of the turning component, at
any given moment, from any initial position of the latter in
relation to the fixed structure. This initial position can vary
from one measurement to another in relation to the fixed structure.
Absolute angular position is understood to be the angle separating
the position of the turning component at any given moment, from a
reference position of the turning component, with this reference
position being fixed in relation to the fixed structure.
As a variant, the determination devices 10 can each consist of an
interpolator increasing the resolution of the respective output
signals, such as described in the document FR-A-2,769,087.
According to one embodiment, one of the determination devices 10
can also be used to determine the angular position of the turning
shaft 1. The value of this position, especially when it is
absolute, can then be used, alone or in combination with the
measurement of the applied torque, in a safety system of the
vehicle, such as a traction control system, antilock brake system,
roll control system, or even a navigation support system.
Moreover, a comparison device 15 of signals derived respectively
from electronic means 13 of each of the determination devices 10 is
provided to ascertain the value of the torque applied to the
turning shaft 1. The device for measuring the torque thus makes it
possible, using the analog signals representing the variation in
the electric field, to generate digital signals S1, S2, that are
next treated in digital form by electronic means 13, then by the
comparison device 15 to obtain the value of the torque applied.
According to the type of sensor 12 used, the device 15 is
constructed to compare either two relative angles or two absolute
angles.
In one embodiment example, the determination devices 10 each
consist of a register initialized at zero under zero torque, and
the comparison device 15 consists of a subtracter of the value of
each of the registers so as to ascertain, according to the nature
of the test body, the value of the torque applied to the turning
shaft 1. The electronic means and the comparison device can be
integrated into a control computer of at least one function of a
car, for example, electric power-assisted steering or path
control.
In the embodiment represented in FIG. 2, the test body 2 is
integrated with a steering column 1 in the form of a zone 16 with
reduced diameter originating from material of column 1. The turning
collars 8 of the bearings 5, 6 are each fixed on one part of column
1 near the first 3 and the second 4 end of the test body 2,
respectively. The steering column 1 is connected on the one hand
with the steering wheel and, on the other hand, with the steering
box, for example, a rack transforming the circular movement of the
steering wheel into angular displacement of the drop arm, which
causes steering of the wheels. The fixed collars 7 of the bearings
5, 6 are connected with a fixed structure, for example, a hollow
tube 17, in which column 1 is arranged for turning.
In the embodiment method represented in FIG. 2, only the fixed
collar 7 of the bearing 6 is connected with tube 17. The fixed
collar 7 of the bearing 5 is assembled so that it slides in said
tube 17. In this embodiment, the whole unit formed from the turning
collars 8 and the column 1 is therefore assembled so that it turns
within fixed tube 17. Moreover, the sensor 12 is connected with the
fixed collar 7 of each of the bearings 5, 6, opposite and away from
the air gap of the multipole ring 11, so that the sensors 12 are
respectively integrated with said bearings 5, 6.
When torque is applied to the steering column 1 through the
steering wheel, the latter transmits the torque to the steering box
by turning at a certain angle. The test body 2, particularly due to
its geometry and/or the nature of the material of which it is
composed, is constructed to transmit the movement of rotation while
undergoing elastic torsion under the action of torque. The result
of this torsion is that the ends 3, 4 of the test body 2, and
therefore of the turning collars 8 connected with them, move by
rotating jointly with column 1 but with an angular displacement of
one with the other, with said displacement increasing
proportionally with the intensity of the torque.
The geometry and/or nature of the material composing the test body
2 are provided so that, on the entire normal zone of use of the
steering column 1, on the one hand the torsion does not exceed the
elastic limit of the material and, on the other hand, the angular
displacement is detectable by the determination devices 10 used.
The sensors 12, by measuring the angular position of each of the
turning collars 8, make it possible to obtain the value of the
torque with these two positions, in particular from the difference
between these two values in the zone of elastic torsion of the test
body 2.
In addition, the measurement of one or both sensors 12 can be used
to determine the relative or absolute position of the column 1 in
relation to the frame of the vehicle. In fact, the angular position
of one of the turning collars 8 corresponds to that of the column
1, namely typically between -4.pi. and +4.pi. in the case or [sic;
where] the steering wheel is expected to make 4 complete turns.
FIG. 3 represents a module 18 for measuring torque applied to a
turning shaft 1, with the module 18 consisting of a torque
measuring device such as that described above. In this figure, one
of the bearings 6 is represented in an exploded view so as to
better show the fixed collar 7, the multipole ring 11, the turning
collar 8, and the rolling bodies 9. The module 18 is designed to be
inserted, possibly immovably, between two parts of a unit to which
the torque to be measured is applied. For this purpose, the module
18 consists of, to the torque measuring device, a means of
connection 19 of said module 18 with this unit.
According to a first variant, module 18 is integrated between two
parts of the steering column 1, with said column lacking the test
body. According to a second variant, module 18 is integrated
between the steering column 1 and the steering wheel, with the
column lacking a test body.
The means of connection 19 represented in FIG. 3, two in number,
are each formed from a grooved part 20, each extending from one of
two sides of the module 18. For example (see FIG. 3), the grooved
parts 20 are provided on one end 21 of a cylindrical part 22 with a
diameter approximately identical to that of the column 1 and the
other end 23 which originated from material with the test body 2.
According to this embodiment, the unit formed from the test body 2
and the connection means 19 is a monobloc casting. The part of the
column and/or the component applying the torque can be made
integral with these two grooved parts 20, respectively,
particularly by force fit, so that the unit thus formed is capable
on the one hand of transmitting the torque and, on the other hand,
of measuring it.
In the module represented in FIG. 3, the turning collar 8 of each
bearing 5, 6 is connected with the test body 2 near its respective
ends 3, 4. Module 18 also consists of a hollow tubular part 24
(represented partially in FIG. 3) with which the fixed collars 7 of
the bearings 5, 6 are connected. The sensors 12 are also connected
with this part 24 in order to be separate from the bearings 5, 6.
Such a module 18 has the advantage of being compact and of forming
an independent unit that may be connected, possibly immovably, with
a unit to which a torque is applied before being transmitted and
measured.
The invention can also be applied to other areas, such as for the
transmission of force, for example, for the wheels of a vehicle,
and for the control of braking of the vehicle by means of the
measurement of the applied torque. In fact, the digital sensors
operate with comparators with thresholds and, because of this, are
less sensitive than the analog sensors of the prior art to
variations in amplitude of the magnetic field. Furthermore, in
order to increase the resolution of the output digital signals,
these magnetic sensors can include a spatial digital interpolator
of the ratiometric type, making it possible to be free of
variations in air gap and drifts of temperature amplitude.
In addition, the invention provides a torque measuring device in
which the magnetic sensors remain fixed during rotation of the
turning shaft. Furthermore, according to the invention, the
measurement function for torque is integrated with two bearings of
the turning shaft using technology of the multipole encoder type so
as to add the function of guiding while rotating shaft in addition
to measuring the torque. This integration simplifies assembly.
* * * * *